Network Address Port Translation (NAPT) is a commonly known packet translation mode, which is commonly used for an access device, and can hide a small or medium sized network behind a legal Internet Protocol (IP) address. The main advantage of the NAPT is being able to use a globally effective IP address to implement universality.
However, in building of access to an extranet which requires keeping a consistent port mapping between an intranet and the extranet, it is necessary to adopt the static NAPT to set the port mappings between the extranet and the intranet one by one. Thus, the problems that too many resources are occupied by static configurations, it is very inconvenient to maintain manually and session resources are occupied will arise.